1. Field of the Invention
The present invention relates to a control valve for a fuel injector, especially an electromagnetically actuated control valve for a fuel injector of an air-compressing, spontaneous-ignition, internal combustion engine; the control valve includes a housing and a valve body in the form of a piston valve which is axially movable in a housing chamber into a closure position and an open position, with the closure position being determined by a valve seat on the housing, and a seating surface edge on the piston valve; the housing chamber includes at least one high pressure connection, and a low pressure connection.
2. Description of the Prior Art
A control valve of this general type for a fuel injector is known from German Offenlegungsschrift No. 30 02 361. On the one hand, this heretofore known control valve controls the injection times (start and finish of injection) by controlling the intake channel of an injection pump, and on the other hand connects a discharge channel with a high pressure channel of the injection pump. The control valve itself is provided with a valve body which is in the form of a piston valve and is provided with a valve seat, with a high pressure chamber (high-pressure side of the piston valve) and a low pressure chamber (low-pressure side of the piston valve) respectively being provided on the two sides of the valve seat. The oppositely disposed pressure attack surfaces of the high pressure and low pressure chambers have different dimensions. Furthermore, a fixed throttle is provided in the discharge channel so that an exact closure position of the piston valve can be assumed without oppositely directed opening movements. For this purpose, an overall considerable manufacturing and assembly cost is required.
However, results show that significant drawbacks are connected with the control valves of the aforementioned type, so that despite the expense of these valves, a precise regulation of the injection process is not possible; furthermore, the operating conditions of the internal combustion engine are altered in a disadvantageous manner. This is based particularly on the fact that during impact of the seating surface edge of the piston valve in the valve seat of the valve housing, unavoidable rebound movements occur. Tolerances with regard to the material, manufacturing, and prestressing of the springs required for the closure process make varying rebound movements unavoidable for multi-cylinder internal combustion engines, for example with the control valves provided per cylinder unit. As a result, there is a distinct lack of uniform conveyance of fuel for the respective cylinder units as a result of the function-related drawbacks of the heretofore known control valves. Furthermore, different rebound movements of the various control valves cause different leakage or lack of sealing in the valve seat. A further drawback of the heretofore known control valves is that the throttled discharge opposes a rapid pressure reduction at the end of injection in the sense of a favorable consumption and emission characteristic of the internal combustion engine; furthermore a fixed value throttling cannot satisfy various operating points of the internal combustion engine due to different closing off at any given time.
An object of the present invention is to provide a control valve for a fuel injector of the aforementioned general type which, while including the material and manufacturing tolerances for which allowance must necessarily be made, while at the same time not adversely affecting the uniform conveyance, and while providing nearly uniform sealing conditions, is in the position to be used in fuel injectors of multi-cylinder internal combustion engines.
This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying drawing.